Thermal barrier coatings (“TBC”) are typically used in articles that operate at or are exposed to high temperatures. Aviation turbines and land-based turbines, for example, may include one or more components protected by the thermal barrier coatings. Under normal conditions of operation, coated components may be susceptible to various types of damage, including erosion, oxidation, and attack from environmental contaminants.
For turbine components, environmental contaminant compositions of particular concern are those containing oxides of calcium, magnesium, aluminum, silicon, and mixtures thereof; dirt, ash, and dust ingested by gas turbine engines, for instance, are often made up of such compounds. These oxides often combine to form contaminant compositions comprising mixed calcium-magnesium-aluminum-silicon-oxide systems (Ca—Mg—Al—Si—O), hereafter referred to as “CMAS.” At the high turbine operating temperatures, these environmental contaminants can adhere to the hot thermal barrier coating surface, and thus cause damage to the thermal barrier coating. For example, CMAS can form compositions that are liquid or molten at the operating temperatures of the turbines. The molten CMAS composition can dissolve the thermal barrier coating, or can fill its porous structure by infiltrating the pores, channels, cracks, or other cavities in the coating. Upon cooling, the infiltrated CMAS composition solidifies and reduces the coating strain tolerance, thus initiating and propagating cracks that may cause delamination and spalling of the coating material. This may further result in partial or complete loss of the thermal protection provided to the underlying metal substrate of the part or component. Further, spallation of the thermal barrier coating may create hot spots in the metal substrate leading to premature component failure. Premature component failure can lead to unscheduled maintenance as well as parts replacement resulting in reduced performance, and increased operating and servicing costs.
However, routine maintenance of a TBC includes washing and reapplying the TBC material onto the component. Such operations require either engine disassembly or an engine wash process such that a new TBC can be applied onto the surface of the component(s). Such a disassembly processes, causes downtime in the engine leading to loss of service for extended periods of time. Alternatively, flushing the internal components of the engine with detergents and other cleaning agents can introduce other unwanted issues to the engine.
Therefore, a process is needed to extend the life of TBC coatings, especially for continued operation of the hot section components of a gas turbine engines, while avoiding any disassembly and/or cleaning processes.